This Demonstration presents a simple test for Kleene's three-valued logic. The values are: True, False, and Undefined (or Unknown or Undecided), with associated numerical values 1, 0, 1/2, respectively. The value of compound propositions is evaluated according to Kleene's truth tables.
A simple two-dimensional area is occupied by triangles, squares, and pentagons of three sizes and two colors. A disk-shaped figure means that the shape of the element is not known. In this case a proposition of type Shape() has value "undefined".